The objective of this research program is the elucidation of the molecular mechanism and the modes of regulation of axonal transport in neurons. Since axonal transport is not only essential to the viability and functioning of the cell, but also probably contributes importantly to long-term modulation of the synapse, it is believed that attainment of the objective could aid in understanding neuronal processes such as synapse formation, use of "trophic" factors, and learning. The approaches of this objective stem from two advantages that are at present uniquely afforded, in the field of axonal transport, by the single neuron preparation of Aplysia californica. First, single cells, which can be recognized as unique individuals from animal to animal, can be studied and, secondly, molecules can be injected directly into the cell, thus permitting the use of pharmacologicalagents which would not have access to the machinery of axonal transport if applied externally. Specifically, there will be three lines of investigation: 1) description of the kinetics of organelle movement in a single axon by study of the transport of 3H-glycoprotein, 2) investigation of the molecular mechanism of axonal transport by determination of the effects on axonal transport of a) injection of specific antibodies to actin, myosin and tubulin, b) injection of the calcium chelator, EGTA, 3) investigation of the regulation of axonal transport by examination of the coupling between physiological activity of the cell and levels of axonal transport.